This invention relates to an open hot water heater which includes a heating vessel having a cold water inlet, a hot water outlet and a device for varying the volume of the heating vessel.
In all known types of hot water heaters in which the water to be heated is stored in a tank and heated, the water will expand during the heating process. The expansion causes pressure to build up inside the tank. To avoid damage during the increase of pressure, it is necessary to use some form of volume compensation in the closed tank.
In hot water heaters found, for example, in the kitchen and/or bathroom of households, where the hot water outlet is an overflow which is connected with a tap, and through which the heated water is driven out by the inflowing cold water when the tap is open, a volume compensation is effected simply by a drop-by-drop escape of the expanded water at the tap. Such an escape of water, however, in an area where the user is often likely to be found during the heating of the water in the vessel, is considered to be a disadvantage in many customer circles, thus tending to limit the sales of a hot water heater with this type of volume compensation.
One way to overcome the aforementioned disadvantage is to conventionally equip the water tank of an open hot water heater with a volume compensation device which prevents the escape of the expansion water during the heating process. Such a device is disclosed in German Patent No. 3,040,450. This type of device has a temperature-dependent setting member which is associated with the water tank. It operates by changing the volume of the water tank according to the temperature-caused change in the volume of the heated water.